SimScale CAE Forum

Best way to model a sphere?

I have tried creating and importing a 1m diameter sphere as both a solid and surface model in the .step format and notice the sphere has a seam and wrinkles at the ends. When I do the hex meshing for CFD, I get an error message “the tesselated surface is not closed”. I’ve reviewed other public projects modeling spheres and it seems they all have this problem unless the sphere was imported as an .stl. What is the best type of sphere model to import to get the best representative hex mesh for CFD? I also noticed when when I proceed with the simulation using the mesh in spite of the warning, the forces on the sphere surfaces were not calculated. I’m wondering if the is related to the meshing issues with the sphere.

Hi @mamboyoyo,

“If you have the choice, STEP is the preferred one since it’s superior in terms of the conversion process to IGES. The STL format can only be used for fluid mechanics analysis since only certain meshing algorithms on SimScale support it.” Source: SimScale documentation

I also looked at other public projects dealing with spheres and they all had the same “seam” that you have.

By the way: Which forces do you mean? The ones from the “Result control” ?

If you need help for the simulation setup, feel free to ask.

P.S: Concerning your question about the warning, @afischer posted a good answer to this a while ago:

“The hexahedral meshing is not based on so called rich geometry formats as for example *.step or *.iges, but on triangulated geometries like e.g. *.stl. In general you should not care about this at all as the triangulation is done automatically prior to the meshing. In some cases, if the geometry model is not “clean”, the triangulation can not be done properly and there might be small cracks or duplicated triangles. The meshing is in general very robust in regards to those defects. That is why your mesh is still valid, but we expose this as a warning as it might help in cases where the mesh result does not look as expected.”



Thanks for the response. I was basically wondering if there was a “best” way to model a sphere, like if it would be preferable to start with a high quality, high triangle count .stl file instead of a .step file to create the hex mesh of the sphere. Judging from your response and the quote, it sounds like it really doesn’t matter and those warnings should not be affecting my results.


Hey Chad,

as mentioned above you are on the right track using .stl files. Try setting up your model once again and if you encounter any problems I will jump in and help you there.

Create another project and also look what the meshing log says. This is also quite helpful if you want to see if there are any glitches in the mesh.

I guess you are trying to investigate the flow around a sphere, right?